I just bought a Jane magnolia tree for the landscaping on the southeast corner of my home. It will get full sun in this spot, but most intense in morning. How close to the house can I plant it? Ideally I don't want a large gap between it and the corner of my home when it is mature.
Washington County Minnesota magnolia
A 'Jane' Magnolia reaches about 15' high x 12' wide at maturity. Note that 12' is in optimal growing conditions (soil, nutrients, water) and note considering potential weather or animal damage that could impact the tree's long-term health and, subsequently, its size.
You can use a rope or garden hose to layout a circle 12-feet in diameter to get an idea of how large the plant can get. I understand you don't want a gap between the tree and the house, but a gap would be better than having to prune the tree excessively and ruin the natural form. It is also not a good idea to have trees rubbing on structures as it can damage the tree and the house siding / windows.
Based on a 12-foot wide mature canopy, I would recommend digging the hole for your tree 9 feet from your house.